The present invention relates to sliders used in hard disk drives. In particular, the present invention relates to sliders having integrated lapping guides.
A slider is a precisely fabricated part that has to carry magnetic sensors for performing reading and writing operations while flying above rotating disks of a hard disk drive. The ever-increasing data storage densities in hard disk drives require precisely fabricated sliders with well-defined magnetic sensor stripe height and the air-bearing surface possessing flatness and surface finish values in the order of nanometers. Such a level of stripe height control as well as slider flatness and surface finish is crucial for the slider to support a reliable and lasting performance of a hard disk drive.
An important fabrication step in the manufacturing of air bearing surfaces is a lapping process during which the air-bearing surface receives its final flatness and surface finish. During the lapping process material is removed from the tool-cut surface. Lapping guides are utilized to control the amount of removed material so that the magnetic sensor has the precise stripe height at the end of lapping process.
The lapping guide is specifically configured to provide enhanced process information about the lapping process. It is commonly deposited as a thin-film stripe so that there exists a well-defined relationship between the lapping guide height and the magnetic sensor stripe height. A lapping guide is shortened as material is being removed from the air-bearing surface. The lapping guide height, EH, is monitored via its resistance value, R, since they are inversely proportional to each other:
EH=K/R. 
The proportional constant, K, is proportional to the electric resistivity of the lapping guide, the width of the lapping guide, and inversely to the thickness of the lapping guide.
The lapping of the air-bearing surface is commonly performed on the so-called row level at which a number of sliders are arranged in a linear array to compose one work piece. Lapping on the row level allows simultaneous lapping of a number of sliders within a single work piece. The lapping guides used in the prior arts are deposited in the kerf regions between sliders and are to be removed after the lapping process. They are not present in the finished slider bodies.
The even removal of material from each individual slider contained in a work piece is hampered by various factors. Such factors include, for example, internal tension and elastic deformation of the work piece resulting from any mounting, cutting, or lapping induced stress or dimensional tolerances among individual work pieces cut from a wafer. To compensate for these factors and to achieve accurate stripe height control, lapping guides need to be placed in proximity to the magnetic sensors. This patent introduces electric lapping guides that are integrated in each individual slider such that the lapping guide and the magnetic sensor are as close as possible. Such an integrated lapping guide has an additional benefit of increasing the wafer utilization efficiency. Furthermore, each slider body may include more than one lapping guide to cancel any adverse effects on stripe-height variations caused by tolerance in the wafer cutting process or the slider lapping process.
U.S. Pat. No. 5,816,890 to Hao et al., for example, shows a method for wiring a number of lapping guides adjacently placed on a number of sliders contained in a work piece.
The work piece is identified as a bar in the patent. The invention addresses the problem of area consumption resulting from the use of lapping guides on the work piece. The area consumption of the lapping guides, peripheral terminals and connecting traces limits the number of sliders that can be fabricated on any given wafer. Hao et al. introduce a wiring configuration that allows to independently recognize the resistance change of individual lapping guides with fewer traces and terminals.
Hao et al. make apparent the dilemma of the commonly used fabrication techniques where an increasing number of lapping guides has to be provided relative to the number of sliders embedded in an work piece in order to meet the increasing demands for lapping accuracy.
Hence, there exists a primary need for providing lapping guides in close proximity to the most critical lapping areas of a slider. On the other hand, there exists also a secondary need for fabrication of closely spaced sliders on a wafer in order to utilize the limited wafer area most efficiently. In view of what is known to those skilled in the art, fulfilling to the primary need may only be accomplished by neglecting the secondary need and vice versa. The present invention allows to comply with the primary need and the secondary need at the same time, as will become apparent from the summary and detailed description below.
The present invention introduces a slider having one or more integrated lapping guides and a method for lapping individual sliders. In accordance with the invention, sliders can be fabricated in close spacing on a wafer. Furthermore, one or more lapping guides can be placed in close proximity to the most critical lapping area around the read/write stack of the slider. The lapping guide(s) can be built into each slider to compensate for the tolerance in slider geometric variations during processing.
The lapping guide(s) is/are deposited as thin film(s) on the back face of the slider. The slider back is a face perpendicular to the lapped surface. The main functional features for reading and writing of data are fabricated from a number of deposited layers on the slider back face, as is well known in the art.
Sliders are commonly designed in a symmetrical fashion with the read/write stack being placed in the center of the back face. In order to provide high acceleration and deceleration of an operational slider, it is desirable to keep the slider mass and therefore the slider size small. It is merely noted that it serves the purpose of an optimally operating hard disk drive to keep the slider back face small even though additional features may be placed on it. Additional features that are necessary to utilize lapping guides on the slider back are conductive leads and terminals to conductively access the lapping guides.
In order to place and operate lapping guides on the tightly dimensioned slider back, the present invention utilizes slider features fabricated for transmitting signals during operational use of the read or write head. Such features are a terminal and leads conductively connected on one side of the write head.
In the preferred embodiment of the invention, two lapping guides are placed in a symmetric fashion lateral to the read/write stack. Wired in parallel, the two lapping guides share two common terminals. One of these two terminals can be a terminal provided for accessing the write head and only one additional terminal with corresponding leads needs to be provided on the sparsely available area on or around a slider back. As a result, a total resistance of two parallelly-connected lapping guides can be measured between the two terminals. The reciprocal value of this total resistance, R_Total, corresponds to the sum of the reciprocal resistances of each of the two individual lapping guides:
1/Rxe2x80x94Total=1/R1+1/R2. 
Lapping of work pieces containing a number of air-bearing surfaces is commonly performed in the industry. The present invention allows for lapping of the individual slider rather than a simultaneous lapping of a number of sliders contained in a work piece. Accordingly, the sliders are cut into individual pieces before the lapping is performed. The symmetric arrangement of the lapping guides relative to the read and write elements provides for a precise observation of the removed material height within the most critical lapping area including and surrounding the read and write elements.
In the preferred embodiment two essentially identical lapping guides are connected in parallel electrically. Any mis-alignment of the air-bearing surface due to either slider cutting or non-uniform lapping will cause opposite effects on the reciprocals of resistance value and will not alter the sum of the reciprocals. As a consequence, the end-point accuracy during the lapping of the relevant areas of the air-bearing surface may be provided regardless eventual skew of the lapping plane relative to the slider. This is, because the conductive bridging of the two symmetrically placed lapping guides compensates for any variations in material remaining from one lapping guide relative to the other. Variations of material remaining occur, where the lapping is unevenly performed due to a skew of the dedicated lapping area of the slider relative to a lapping plane defined by the lapping apparatus as is well known to those skilled in the art. The placement of lapping guides on the slider back face provides for an economic lapping with increased precision and reliability regardless of any lapping plane skew or clamping imprecision due to the relatively small size of individual sliders.